The Group of 20 (G20) leading industrialized nations kicked off their two-day meeting in Rome on Saturday with climate action ahead of the COP26 summit and the coronavirus likely to dominate.

In his opening speech, Italian Prime Minister Mario Draghi urged greater international cooperation on pressing issues as protectionism and nationalism had been on the rise even before the pandemic.

"Multilateralism is the best answer to the problems we face today," he said.

"In many ways it's the only possible answer. From the pandemic to climate change to fair and equitable taxation, going it alone is simply not an option."

Draghi praised the agreement on a global corporate tax reform reached by the G20 finance ministers in advance.

"We reached a historic agreement for a fairer and more effective international tax system," Draghi said ahead of talks between world leaders in Rome.

The agreement sets a minimum tax of 15 per cent on major multinational corporations, a major overhaul of the existing rules that have long been criticized as encouraging tax evasion.

Draghi also pledged commitment to the WHO's target of vaccinating two-thirds of the world's population against the coronavirus by the middle of next year.

However, he criticized the large differences in vaccination rates between countries, saying there were "startling disparities in the global distribution of vaccines."

While about 70 per cent of the population in rich countries have received at least one dose, this figure stood at roughly 3 per cent in the poorest nations, he said.

"These differences are morally unacceptable and undermine the global recovery."

The G20 meeting in Rome comes right before the UN climate summit in Glasgow and UN Secretary General Antonio Guterres believes the fight against climate change could be lost if the G20 does not step up.

"There is a serious risk that Glasgow will not deliver," he said.

Ahead of the G20 meeting, Rome police cleared an early morning protest staged by a dozen climate activists who had blocked a multi-lane road near the Environment Ministry that provides access to the summit venue, police said.

According to the ANSA news agency, protesters yelled, "If nothing changes, we will block the city."

Two rallies are scheduled for the afternoon with thousands of people expected to attend.

The G20 meeting is being attended by world leaders like US President Joe Biden, while some other leaders such as Russia's Vladimir Putin are taking part via video link.

Germany is represented by caretaker Chancellor Angela Merkel who landed in Rome on Saturday to attend a G20 summit for the last time.

Merkel is in the Italian capital together with her presumptive successor Olaf Scholz, as they aim to send a signal of continuity to Germany's international partners.

The G20 meeting opened with the heads of state and government taking a photo with health-care workers who have been on the front lines of the coronavirus pandemic.

The G20 leaders traditionally take a "family photo" at the start of their annual summit. But this year doctors, nurses and paramedics joined them on the podium as the politicians offered their applause.

The workers, some wearing white lab coats and others the reflective uniforms of paramedics, stood side by side with the leaders.

Italy, this year's G20 host nation, was one of the countries hardest hit by the pandemic in Europe last year.

dpa